Why are we suddenly assaulted by tell-all political autobiographies? Why did Cherie Blair mention her "unmentionables" and put all her other feelings and thoughts on such open display? Why did John Prescott offer us account of his bulimia and sexual peccadillos? What is Lord Levy doing, turning publicly on the very person, Tony Blair, who first propelled him into the limelight? As for the first two, it might be said that they both needed or wanted money, and to get it had to include gossipy items in what they wrote. All three, it could be argued, were motivated also by the settling of scores, mostly personal and mostly petty, but with a sufficient edge of cattiness to get public attention.

Well, yes: but perhaps amid the soap-opera style trivia there is something much more interesting and profound going on. The philosopher Michel Foucault observed that 'We have become a singularly confessing society. The confession spreads its wings far and wide ... one confesses one's sins, one's thoughts and desires, one's illnesses and troubles; one goes about telling, with the greatest precision, what is most difficult to tell'. Foucault traces the tendency to bare all back to the Middle Ages, where it had its origins in the Catholic confessional. It has become a form of truth, he argued, progressively displacing the myths of bravery, courage and marvellous deeds that dominated previous eras and other cultures.

Foucault died in 1984, before the internet took off and before the age of celebrity had really got going. That age introduces a massive generalisation of the confessional principle, now completely secularised. Everything the celebrity does has to be visible, as part and parcel of what celebrity is. This is the reason why those who become celebrities talk endlessly of the intrusions of the media, of their inability any longer to be a private citizen, yet at the same time are hopelessly addicted to the very processes about which they complain. Cherie turns to the press as she and Tony are leaving Downing Street for the last time, and says to the assembled media, "I won't miss you", yet here she is a few months later all over the newspapers and TV, and deliberately so.

None of the three has won much public sympathy - to the contrary - and each has turned against the other. This is par for the course too, since telling the truth, or one's version of it, inevitably turns one against others. Lord Levy says that Tony Blair several times told him that Brown could not defeat David Cameron in an election. Blair himself has denied he ever made such comments, while his wife asserts that Levy doesn't know what he's talking about. John Prescott, having proudly admitted he once called Tony Blair a "little shit", says of Booth's decision to publish her book earlier than originally planned that "she's a daft woman". Levy says he warned Blair about the "long massages" he was having with Carole Chapin, while Cherie asserts that it was at her recommendation.

One might say of all this that it demeans politics in general, and New Labour in particular - as did Alastair Campbell's diaries, which have virtually no discussion of policies or of the substance of politics. No man is respected by his valet, they used to say; and now all of us are witness to the frailties and the all-too-human qualities of those who govern us. Can politicians ever be effective leaders again when the "necessary mystery" of political authority of which Bagehot spoke has evaporated completely?

What is happening here is happening almost everywhere. The intimacies of President Clinton's life were dissected in unsparing detail. In France until recently, political leaders were allowed a private life and in return manifested a certain public dignity; now Mr Sarkozy and his new wife (as well as his old one) are all over the gossip magazines. Silvio Berlusconi in Italy makes no secret of his hair transplants, and his plastic surgery; while President Putin in Russia poses topless for the photographer.

Back to Foucault, who says that the confessional is not a form of truth - not, as it might appear to be, a way of gaining redemption. "The obligation to confess is now relayed through so many different points, is so deeply ingrained in us that we no longer perceive it as the effect of a power that constrains us ..." Speaking specifically of sexuality, he says that instead of imagining that we can achieve freedom by confessing all, by making public all that is private, we can do so only by escaping from sexuality, by breaking the hold it has on our lives.

What would be the equivalent in the sphere of politics? One point that could be made is that integrity often consists less in revealing all than in staying silent. Not for nothing did a distinguished ex-judge say that Cherie's position in the judiciary could be challenged; not for nothing was Sir Christopher Meyer's tell-all account of his time as ambassador in Washington thought distasteful by his Foreign Office colleagues. A certain dignity (even honour?) could perhaps be restored to politics by an active refusal of the confessional. A calculated revision of the laws of privacy, taken over and internalised by those in the public eye might help.

More generally, perhaps, we should review the principle that greater transparency always serves a democratic purpose, no matter how intuitively correct it might seem. It is striking that those organisations which people trust most - the judiciary, medical profession, the army and the police - are those which to some extent manage to keep themselves to themselves.